Use the RAID classes to calculate btrfs sizes (#1264696)
Use the RAID classes to calculate btrfs sizes (#1264696)

We already have a bunch of a RAID size calculcation code, so use that
for the raid modes of btrfs volumes.

rhinstaller/blivet,AdamWill/blivet,rhinstaller/blivet,rvykydal/blivet,jkonecny12/blivet,vpodzime/blivet,rvykydal/blivet,jkonecny12/blivet,AdamWill/blivet,vojtechtrefny/blivet,vpodzime/blivet,vojtechtrefny/blivet